Cytoplasmic synthesis of soluble and mitochondrial malate dehydrogenase isozymes in maize.

The effects of cycloheximide and chloramphenicol on the incorporation of radioactive leucine into trichloroacetic acid-insoluble material and on malate dehydrogenase (MDH) activity in maize scutella were studied. In 40 h of treatment, chloramphenicol (0.5 – 2.0 mg/ml) does not inhibit the increase of either soluble (s) or mitochondrial (m) malate dehydrogenase isozymes. However, 8 h following the addition of cycloheximide (2–10 μg/ml), the usual increase of total malate dehydrogenase activity is reduced by more than 70%. The reduction in the activity of the soluble and the mitochondrial malate dehydrogenase isozymes is similar. From these observations, and from our former studies on this system, we conclude that both the soluble and the mitochondrial malate dehydrogenases are synthesized on cytoplasmic ribosomes.